package com.tyrone.concurrent.lock;

import java.util.concurrent.TimeUnit;
import java.util.concurrent.locks.AbstractQueuedSynchronizer;
import java.util.concurrent.locks.Condition;
import java.util.concurrent.locks.Lock;

/**
 * 独占锁（同一时间只能有一个线程获得锁）
 * 实现自定义同步器组件 实现Lock接口，并且有同步器(Sync)。
 *
 * @author xieyl
 * @create 2021/12/7 22:04
 */
public class Mutex implements Lock {

    /**
     * 继承并重写同步器中的父类方法，AQS中还提供许多模板方法供自定义组件使用。
     */
    private static class Sync extends AbstractQueuedSynchronizer {
        @Override
        protected boolean tryAcquire(int arg) {
            if (compareAndSetState(0, 1)) {
                setExclusiveOwnerThread(Thread.currentThread());
                return true;
            }
            return false;
        }

        @Override
        protected boolean tryRelease(int arg) {
            if (getState() == 0) {
                throw new IllegalMonitorStateException();
            }
            setExclusiveOwnerThread(null);
            setState(0);
            return true;
        }

        Condition newCondition() {
            return new ConditionObject();
        }

    }

    private final Sync sync = new Sync();

    @Override
    public void lock() {
        sync.acquire(1);
    }

    @Override
    public void lockInterruptibly() throws InterruptedException {
        sync.acquireInterruptibly(1);
    }

    @Override
    public boolean tryLock() {
        return sync.tryAcquire(1);
    }


    @Override
    public void unlock() {
        sync.release(1);
    }

    @Override
    public Condition newCondition() {
        return sync.newCondition();
    }

    @Override
    public boolean tryLock(long time, TimeUnit unit) throws InterruptedException {
        return sync.tryAcquireNanos(1,unit.toNanos(time));
    }
}
